Learn Finnish: Vien mekon ompelimoon huomenna. - I will take the dress to the tailor shop tomorrow.

The base is the verb ommella (to sew). The location suffix -mo is added to the strong stem of the verb, ompeli-, to create ompelimo (a place where sewing happens, like a tailor shop). Finally, the -on ending is the illative case, meaning into or to the shop.

Wait, the verb for sewing is ommella. Where does the p in ompelimo come from?

This is due to consonant gradation. The verb ommella has a weak consonant cluster mm in its dictionary form. However, its strong stem uses mp, which you might recognize from the present tense form ompelen (I sew). Derivations like -mo usually attach to this strong vowel stem.

Why does the word mekko (dress) end in -n here?

Because it is the object of the sentence and the action is a complete whole. Taking the dress to the shop is an action you will fully finish. Therefore, the object takes the total object marker -n (the genitive-accusative case), making it mekon.

I usually translate the English word 'take' as ottaa. Why is the verb vien used here?